The present invention relates to nanocapsules based on dendritic polymers and to cosmetic and/or dermatological compositions containing them.
The encapsulation or absorption of lipophilic active principles in particles of submicron size has been known for several years and is widely used in particular in cosmetology and dermatology, since these particles, known as nanoparticles, are capable of crossing the superficial layers of the stratum corneum and of penetrating into the upper layers of the live epidermis to release the active principle therein. This penetration into deeper layers broadens the space of action of the active principles and obscures them from rapid removal by simple rubbing.
The term xe2x80x9cnanoparticlesxe2x80x9d primarily encompasses two different systems: xe2x80x9cnanospheresxe2x80x9d consisting of a porous polymer matrix in which the active principle is absorbed and/or adsorbed, and xe2x80x9cnanocapsulesxe2x80x9d with a structure of core-envelope type, i.e. a structure consisting of a lipid core forming or containing the active principle, this core being encapsulated in a water-insoluble continuous protective envelope. The present invention relates solely to this second vesicular type of nanoparticle, i.e. nanocapsules with a lipid core surrounded by a polymer membrane.
The encapsulation of active principles in capsules of submicron size makes it possible, admittedly, to convey the active molecules more deeply into the skin, but it does not always affordxe2x80x94contrary to what this xe2x80x9cprotectivexe2x80x9d structure might lead one to thinkxe2x80x94sufficient stability of the active principle with respect to the surrounding physicochemical conditions.
The problem of the instability of the active principle arises in particular for substances that are sensitive to oxidation, light, high temperatures and/or acidic or basic pHs. Such a substance which is very commonly used in cosmetics is, for example, retinol (vitamin A1), which is sensitive to oxidation, in particular at acidic pH.
One approach for stabilizing retinol consists in adding lipophilic antioxidants and chelating agents to compositions containing it and in adjusting the pH of these compositions to a value of between 5 and 10 (WO 96/31194).
The Applicant has now discovered that encapsulation in nanocapsules based on a specific type of polymer significantly improves the stability of retinol, and does so in particular in the absence of antioxidants and at pH values below 5.
The polymers which allow such a favourable effect to be obtained are known as dendritic polymers. These polymers have a structure of hyperbranch polyester type which will be described in greater detail hereinbelow.
Thus, the encapsulation of retinol in nanocapsules with an envelope formed from dendritic polymers of the type described above gives this active molecule satisfactory stability, i.e. a loss of activity of less than 20% after storage for 1 month at 45xc2x0 C., whereas, under equivalent conditions, this same molecule encapsulated in other polymers commonly used for nanoencapsulation (for example polycaprolactone or cellulose derivatives) shows a loss of activity at least equal to 30% and possibly being as much as 100%.
One subject of the invention is thus nanocapsules consisting
of a lipid core forming or containing a lipophilic active principle, and
of a water-insoluble continuous envelope comprising at least one dendritic polymer of polyester type containing terminal hydroxyl functions.
A subject of the invention is also cosmetic and/or dermatological compositions containing the said nanocapsules based on dendritic polymers.
Another subject of the invention is a process for preparing nanocapsules based on the above dendritic polymers.
Other subjects will become apparent on reading the description and the examples which follow.
Dendritic polymers or dendrimers (from the Greek dendron=tree) are xe2x80x9carborescentxe2x80x9d polymer molecules, i.e. highly branched polymers, which were invented by D. A. Tomalia and his team at the start of the 1990s (Donald A. Tomalia et al., Angewandte Chemie, Int. Engl. Ed., vol. 29, No. 2, pages 138-175). They are molecular structures constructed around a central unit which is generally multivalent. Linked around this central unit, in concentric layers and according to a fully defined structure, are branched chain-extending units thus giving rise to monodisperse symmetrical macromolecules of well-defined chemical structure and stereochemistry.
The dendritic polymers constituting the envelope of the nanocapsules of the present invention are hyperbranched polymers with the chemical structure of a polyester and which are terminated with hydroxyl groups optionally modified with at least one chain-terminating agent. The structure and preparation of such polymers is described in patent applications WO-A-93/17060 and WO 96/12754.
More specifically, the dendritic polymers used in the compositions of the present invention can be defined as being highly branched macromolecules of polyester type, consisting
of a central unit derived from an initiator compound bearing one or more hydroxyl functions (a),
of chain-extending units derived from a chain-extending molecule bearing a carboxyl function (b) and at least two hydroxyl functions (c), each of the hydroxyl functions (a) of the central molecule being the starting point of a polycondensation reaction (by esterification) which starts with the reaction of the hydroxyl functions (a) of the central molecule with the carboxyl functions (b) of the chain-extending molecules, and then continues by reaction of the carboxyl functions (b) with the hydroxyl functions (c) of the chain-extending molecules.
A xe2x80x9cgeneration Xxe2x80x9d dendrimer refers to a hyperbranched polymer prepared by X condensation cycles, each cycle consisting in reacting all of the reactive functions of the central unit or of the polymer with one equivalent of a chain-extending molecule.
The initiator compound bearing one or more hydroxyl functions and forming the central unit around which the dendritic structure will be constructed is a monohydroxy, dihydroxy or polyhydroxy compound. It is generally chosen from
(a) a monofunctional alcohol,
(b) an aliphatic, cycloaliphatic or aromatic diol,
(c) a triol,
(d) a tetrol,
(e) a sugar alcohol,
(f) anhydro-ennea-heptitol or dipentaerythritol,
(g) an xcex1-alkylglycoside,
(h) a polyalkoxy polymer obtained by polyalkoxylation of one of the alcohols (a) to (g), with a molar mass of not more than 8000.
As examples of preferred initiator compounds for preparing the dendritic polymers used in the present invention, mention may be made of ditrimethylolpropane, ditrimethylolethane, dipentaerythritol, pentaerythritol, an alkoxylated pentaerythritol, trimethylolethane, trimethylolpropane, an alkoxylated trimethylolpropane, glycerol, neopentyl glycol, dimethylolpropane or 1,3-dioxane-5,5-dimethanol.
These hydroxylated initiator compounds forming the central unit of the future dendrimer are reacted with molecules referred to as chain-extending molecules, which are compounds of monoacidic diol type chosen from
monocarboxylic acids comprising at least two hydroxyl functions, and
monocarboxylic acids comprising at least two hydroxyl functions, one or more of which bear(s) a hydroxyalkyl substituent.
Preferred examples of such compounds are dimethylolpropionic acid, xcex1,xcex1-bis(hydroxymethyl)butyric acid, xcex1,xcex1,xcex1-tris(hydroxymethyl)acetic acid, xcex1, xcex1-bis(hydroxymethyl)valeric acid, xcex1,xcex1-bis(hydroxy)-propionic acid and 3,5-dihydroxybenzoic acid.
According to one particularly preferred embodiment of the present invention, the initiator compound is chosen from trimethylolpropane, pentaerythritol and an ethoxylated pentaerythritol, and the chain-extending molecule is dimethylolpropionic acid.
Some of the terminal hydroxyl functions of the dendritic polymers of polyester type used in the nanocapsules of the present invention can bear substituents derived from at least one chain-terminating agent.
The fraction of these terminal hydroxyl functions bearing a chain-terminating unit is generally between 1 and 90 mol %, preferably between 10 and 50 mol %, relative to the total number of terminal hydroxyl functions.
The choice of a suitable chain-terminating agent makes it possible to modify as desired the physicochemical properties of the dendritic polyesters used in the compositions of the present invention.
The said chain-terminating agent can be chosen from a wide variety of compounds capable of forming covalent bonds with the terminal hydroxyl functions.
These compounds encompass, in particular:
i) saturated or unsaturated, aliphatic or cycloaliphatic monocarboxylic acids (or anhydrides),
ii) saturated or unsaturated fatty acids,
iii) aromatic monocarboxylic acids,
iv) diisocyanate monomers or oligomers or addition products thereof,
v) epihalohydrins,
vi) glycidyl esters of a monocarboxylic acid or of a C1-24 fatty acid,
vii) glycidyl ethers of C1-24 monovalent alcohols,
viii) addition products derived from a saturated or unsaturated, aliphatic or cycloaliphatic mono-, di- or polycarboxylic acid, or from the corresponding anhydrides,
ix) addition products derived from an aromatic mono-, di- or polycarboxylic acid or from the corresponding anhydrides,
x) epoxides of an unsaturated C3-24 monocarboxylic acid or of a corresponding triglyceride,
xi) saturated or unsaturated, aliphatic or cycloaliphatic monofunctional alcohols,
xii) aromatic monofunctional alcohols,
xiii) addition products derived from a saturated or unsaturated, aliphatic or cycloaliphatic mono-, di- or polyfunctional alcohol, and
xiv) addition products derived from an aromatic mono-, di- or polyfunctional alcohol.
Examples of chain-terminating agents which may be mentioned are lauric acid, linseed fatty acids, soybean fatty acids, tallow fatty acids, dehydrogenated castor oil fatty acids, crotonic acid, capric acid, caprylic acid, acrylic acid, methacrylic acid, benzoic acid, para-tert-butylbenzoic acid, abietic acid, sorbinic acid, 1-chloro-2,3-epoxypropane, 1,4-dichloro-2,3-epoxybutane, epoxidized soybean fatty acids, trimethylolpropane diallyl ether maleate, 5-methyl-1,3-dioxane-5-methanol, 5-ethyl-1,3-dioxane-5-methanol, trimethylolpropane diallyl ether, pentaerythrityl triallyl ether, pentaerythrityl triacrylate, triethoxylated pentaerythrityl triacrylate, toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, hexamethylene diisocyanate or isophorone diisocyanate.
Among the chain-terminating agents which are particularly preferred are capric acid and caprylic acid or a mixture thereof.
The dendritic polymers of polyester type containing terminal hydroxyl functions and optionally bearing chain-terminating groups are known and are sold by the company Perstorp.
Among the polymers which it is particularly preferred to use in the present invention are
a dendritic polyester obtained by polycondensation of dimethylolpropionic acid with trimethylolpropane and which is free of chain-terminating agents, for example the product sold under the name xe2x80x9cBoltorn(copyright) H40 (TMP core)xe2x80x9d by the company Perstorp;
a dendritic polyester obtained by polycondensation of dimethylolpropionic acid with polyoxyethylenated pentaerythritol (on average 5 units of ethylene oxide to each hydroxyl function), which is free of a chain-terminating agent, for example the product sold under the name xe2x80x9cBoltorn(copyright) H30xe2x80x9d by the company Perstorp;
a generation 3 dendritic polyester obtained by polycondensation of dimethylolpropionic acid with polyoxyethylenated pentaerythritol (on average 5 units of ethylene oxide to each hydroxyl function), 50% of the hydroxyl functions of which are esterified with C8-10 acids and in particular capric(C10) acid and caprylic(C8) acid (xe2x80x9cBoltorn(copyright) H30 (esterified)xe2x80x9d sold by the company Perstorp).
Among these three polymers, the last one is the one most particularly preferred.
These dendritic polymers are used to prepare nanocapsules consisting of a lipid core forming or containing an active principle surrounded by an envelope formed by these polymers.
The process for preparing nanocapsules which is used by the Applicant Company is preferably the one described in EP-A-0 274 961. It comprises the steps consisting in
dissolving the polymer, the lipid phase forming or containing the active principle and optionally a surfactant acting as a coating agent, in a suitable organic solvent, i.e. a solvent which is miscible with water, non-toxic and more volatile than water (generally acetone and/or a lower alcohol),
preparing a solution of a suitable surfactant in water (non-solvent for the polymer and the lipid phase),
pouring the organic phase into the aqueous phase while stirring the latter phase moderately, which results in the spontaneous formation of an emulsion of nanocapsules,
and then evaporating the organic phase and, possibly, some of the aqueous phase, which gives a concentrated suspension of nanocapsules in an aqueous phase.
This preparation process generally involves heating the organic phase and/or the aqueous phase to temperatures of between 35 and 70xc2x0 C. The dendritic polyesters used in the present invention allow this process to be carried out at room temperature, which constitutes a considerable advantage in particular for heat-sensitive active substances such as retinol.
The surfactant serves primarily to control the size of the nanocapsules. It does this by stabilizing the nanocapsules in the emulsion resulting from pouring the acetone phase into the aqueous phase and preventing them from coalescing.
Any surfactant of hydrophilic nature can be used, whether it is a nonionic, anionic or cationic surfactant. Examples which may be mentioned are sodium lauryl sulphate, quaternary ammonium compounds, sorbitan monoesters which may or may not be polyoxyethylenated, fatty alcohol ethers of polyoxyethylene glycol, condensates of ethylene oxide and of propylene oxide, such as the product Pluronic(copyright) F-68 sold by the company BASF, or phospholipids such as lecithin.
The weight ratio of the surfactant to the materials constituting the nanocapsules is advantageously between 0.01 and 0.5 and preferably in the region of 0.2.
It is often desirable or necessary to provide the nanocapsules with a so-called xe2x80x9clamellarxe2x80x9d coat. This is a structure organized into one or more lipid leaflet(s) each consisting of a bilayer of amphiphilic molecules which are similar to that of biological membranes. Besides its function of adjusting the size of the nanocapsules, this coat improves the leak-tightness of the nanocapsules with respect to a leakage of the active principle towards other lipid phases of the composition.
The coating agents are surfactants of hydrophobic nature that are soluble in the organic phase used in the present process and that are capable, in the presence of water, of forming the lipid bilayers described above. In the process for encapsulating active principles which is used by the Applicant Company, this coating agent is dissolved in the organic phase (acetone/alcohol) containing the polymer and the lipid phase.
Examples of coating agents which may be mentioned are phospholipids such as lecithin, according to patent application EP-A-447 318, certain polycondensates of ethylene oxide and of propylene oxide, such as the products sold under the name Pluronic(copyright) by the company BASF, such as Pluronic 121, or under the name Synperonic(copyright) by the company ICI, or certain silicone surfactants, such as those described in documents U.S. Pat. Nos. 5,364,633 and 5,411,744 and used in patent application FR-A-2 742 677, for example those sold by the company Dow Corning under the names DC 5329, DC 7439-146, DC 2-5695 and Q4-3667.
The size of the nanocapsules based on dendritic polymers thus obtained is advantageously between 50 and 800 nm, preferably between 100 and 300 nm.
The nanoencapsulation process of the present invention allows the encapsulation of any kind of lipophilic cosmetic or dermatological active principles.
Examples which may be mentioned are emollients, anti-inflammatory agents, antibacterial agents, antifungal agents, antiviral agents, anti-seborrhoeic agents, anti-acne agents, keratolytic agents, antihistamines, anaesthetics, cicatrizing agents, pigmentation modifiers, sunscreens, free-radical scavengers, moisturizers, vitamins and other similar lipophilic compounds.
According to the present invention, the encapsulated active principle is preferably a lipophilic active principle that is sensitive to the surrounding physicochemical conditions such as the temperature, the pH, light or the presence of oxidizing agents.
Examples of preferred lipophilic active principles which may be mentioned are vitamins such as vitamin A (retinol) or esters thereof, vitamin E or esters thereof, such as tocopheryl acetate, vitamin D or derivatives thereof and vitamin F or derivatives thereof, carotenes such as xcex2-carotene or derivatives thereof such as lykopene, and salicylic acid or derivatives thereof, in particular those described in documents FR-A-2 581 542, EP-A-378 936 and EP-A-570 230, in particular 5-n-octanoylsalicylic acid, 5-n-decanoylsalicylic acid, 5-n-dodecanoylsalicylic acid, 5-n-octylsalicylic acid, 5-n-heptyloxysalicylic acid and 4-n-heptyloxysalicylic acid.
Excellent results have been obtained in particular for the encapsulation of retinol (vitamin A1), which is a molecule that is very sensitive to oxidation at acidic pH, as well for the C1-30, more particularly C1-6, esters thereof, such as retinyl acetate and retinyl propionate.
A subject of the present invention is also cosmetic and/or dermatological compositions containing, in a physiologically acceptable support, the nanocapsules based on dendritic polymers described above.
The fraction represented by the nanocapsules in the cosmetic and/or dermatological compositions of the present invention is generally between 0.1 and 30% by weight and preferably between 0.5 and 15% by weight relative to the total weight of the composition.
In addition to the nanocapsules and the aqueous phase, the compositions can contain known cosmetic and/or pharmaceutical adjuvants such as fatty substances, petroleum jelly, pH regulators, preserving agents, thickeners, dyes or fragrances.
Needless to say, a person skilled in the art will take care to select this or these optional additional compound(s) and the amount thereof, such that the advantageous properties intrinsically associated with the cosmetic or dermatological composition in accordance with the invention are not, or are not substantially, adversely affected by the addition(s) envisaged.
The compositions according to the invention can be, for example, in the form of a serum, a lotion, an aqueous, aqueous-alcoholic or oily gel, a water-in-oil or oil-in-water emulsion or in the form of aqueous dispersions of lipid vesicles consisting of ionic or nonionic lipids or of a mixture thereof, these vesicles possibly containing an oily phase.
The examples given below, purely for illustrative and non-limiting purposes, will make it possible to gain a better understanding of the invention.